Rectifier for television signals



21, 1940- K, SCHLEVSINGER 2,201,794

RECTIFIER FOR TELEVISION SIGNALS Filld latch 13. 1937 In men for:

Patented May 21,. 1940 om'rn PAT NT OFFICE RECTIFIER FOR TELEVISIONSIGNALS Kurt Schlesinger, Berlin, Germany, assignor, by mesneassignments, to Loewe Radio, Inc., a corporation of New York ApplicationMarch 13, 1937, Serial No. 130,718 In Germany March 19, 1936 2 Claims.

lZhe present invention relates to television circuit arrangements andmore particularly to television rectifying circuit with anafter-connected amplifier-stage and most effective suppression of thecarrier-frequency oscillations.

The object of a rectifier in respect of the modulated ultra-short waveor the modulated intermediate-frequency Wave of a television superhet isas follows: Inertialess operation in demodu- -'-lating up to maximumfrequency of the image,

the image-point traversing period; further, at least linear response toincreasing amplitudes of the carrier wave, and preferably more thanlinear response, 1. e., increasing slope of the char- .acteristic curvein the case of increasing amplition have all these features necessaryfor good operation and more particularly the present invention isdirected to complete elimination of the carrier-frequency-oscillationsin the circuits after-connected to the rectifying stage.

In the accompanying drawing embodiments of the circuits according to thepresent invention are shown.

Fig. 1 shows a television receiving circuit according to the presentinvention and Fig. 2 represents a diagram of the circuit shown in Fig. 1showing the relations between the potential at the grid of the Brauntube and the frequencies to be transmitted.

As well known, the increasing slope of the characteristic withincreasing amplitudes is performed by use of anode bend rectification,primarily with short-circuiting of the anode circuit. A three-pole tubeI, with the aid of a tapping 3, is so adjusted to a battery 2 having acomparatively low potential of approximately 30 volts that the anodecurrent is just caused to cease. The modulated carrier wave is suppliedby means of the transformer 4. In the anode circuit there is provided aresistance 5, which is made so small in its ohmic value that in spite ofthe inherent capacities it is effective also at the highestimage-frequencies. An after-connected amplifying tube 6 is coupled withthe anode of tube I in direct fashion. The grid 1 is preferably passedout separately through the glass wall. The cathode of the amplifier 6 isearthed, and the tube itself is a pentode with large amplificationfactor.

In both anode circuits, that of the detector I and that of theafter-amplifier 6 with its anode resistance 8, there arise bothrectified modulated oscillations as well as considerable traces of thecarrier-oscillations. The anode circuit of the end amplifier is notconnected through to the Braun tube 9 directly, but the carrier wave ispreviously eliminated by a capacitative compensation. For this purpose adifferential condenser l0/H is connected with one pole to the anodecircuit 8 and with the other pole to the grid 1 of the am- 16 plifier 6.The rotor l2 may then be so adjusted that the carrier wave disappearsentirely. A condition for this is that there is not caused by reason ofthe useful circuit I3/ I4 any inadmissible load on the condenser portionl0/ l2. Merely go the image currents flow through the circuit l3/ l4.According to the invention, the circuit is produced as series connectionof a choke l3 and a damping resistance M. It is then possible to find achoke operating in series resonance with u the inherent capacities l5 atthe maximum image frequency. As regards all frequencies which are stillhigher, i. e., more particularly beyond the side band of the carrierwave, the choke then represents a very high resistance, and accordinglythe compensation by the differential condenser is very good for thecarrier wave.

Fig. 2 shows a diagram showing the relationship (experimentallyobtained) between the oscillation potential e at the control grid 9 ofthe image reproducing device of the circuit of Figure 1 over awave-length band between 50 metres and approximately 300 metres. Thecarrier wave-length was 100 m., side band about 50 to 150 m., the numberof lines per frame was 400 and the maximum video frequency in was 1.6 10which corresponds to about 200 m. Choke I3 had a winding surface of 100xmm., and was arranged to resonate at frequency in.

The oscillation potential e at the grid 9 of the 5 of a resonance humpin the neighbourhood of 5 the frequency is. The shape of the resonancehump at frequency ,fB can be varied by varying the value of resistancel4. Curve a was obtained with the damping resistance M at zero,

curve b was obtained with resistance M at 2,000

| 200 lines 20 The neutralisation capacity 10/ l! remains constant,independently of the number of lines, so long as the branch l3/8 in thecase of maximum image frequency is adjusted to series resonance and atthe same time possesses a sufficiently high impedance.

The synchronisation is branched off at the line which is traversed bythe most powerful modulation frequencies, as it is there that theamplitude filtering is possible in the most simple 0.5fashion. It ispreferably performed by a twopole tube is having a free cathode, whichoperates by way of an adjustable bias H on the synchronisationtransformers is. It is preferable and possible to fit this two-pole pathinto the -I three-pole tube l, as merely a very small emission ofapproximately 2 milliamperes is required in respect of the two-poletube.

I claim:

1. In combination an electronic amplifier including at least an anode, acontrol grid and a cathode, having an input and output circuit, a filtercircuit and means for balancing out carrier frequency oscillations, saidfilter circuit and said means being arranged in said output circuit,said 5 means for balancing out consisting of a diilerential condenserhaving one rotor and two stators, one stator being connected to saidinput circuit which rectified carrier oscillations with modulationsignals are applied to, the other stator being connected to the anode ofsaid amplifier, said rotor being connected to the output terminal ofsaid amplifier, said filter circuit being arranged between said statorconnected to said anode and said rotor and having a low impedance to themodulation signals and a high impedance to the carrier oscillations.

2. In combination an electronic amplifier including at least an anode, acontrol grid and a cathode, having an input and output circuit, a filtercircuit and means for balancing out carrier frequency oscillations, saidfilter circuit and said means being arranged in said output circuit,said means for balancing out consisting of a difierential condenserhaving one rotor and two stators, one stator being connected to saidinput circuit which rectified carrier oscillations with modulationsignals are applied to, the other stator being connected to the anode ofsaid amplifier, said rotor being connected to the output terminal ofsaid amplifier, said filter circuit being arranged between said statorconnected to said anode and said rotor and consisting of aself-inductance and a damping resistance in selies-connection, saidself-inductance resonating 3 at the highest modulation-frequency to anextent which is adjustable by varying the value of the dampingresistance.

KURT SCI-ILESINGER.

